a diplomonad, a small zooflagellate (protozoan) that inhabits the digestive system of various animals
unicellular, lacks mitochondria
has two nuclei bounded by nuclear envelopes, a cytoskeleton, and multiple flagella
pear shaped and has one or two claw-shaped median bodies (13)
Relationship to humans
parasite that contaminates water supplies and causes the intestinal disease giardiasis
one of the most common causes of waterborne disease in humans worldwide
can cause chronic diarrhea and growth retardation in children of developing countries, more commonly infects children than adults, dangerous to those with malnutrition, immunodeficiencies, or cystic fibrosis (12).
first protozoan parasite described, thought to be a harmless commensal organism of the intestine until 1970s, when it appeared in community outbreaks and travelers returning from developing countries (12)
Habitat and niche
found in soil, food, water, or any surface that has been contaminated with feces from an infected animal
can often be found in water that has not been boiled, filtered, or disinfected with chemicals
After entering the host, it lives and reproduces in the small intestine, attaching itself to the epithelium using its ventral adhesive disc (2), a concave structure containing contractile proteins that aid in the organism's attachment (14).
Predator avoidance
can switch surface proteins to avoid detection by the human immune system, making it difficult for human bodies to clear Giardia infection without drug treatment
a protective outer shell protects it from disinfectants containing chlorine (8).
Nutrient acquisition
uses a sucking disk to get nutrients from the mucous membrane of the small intestine of its host (2)
aerotolerant anaerobe: doesn't require oxygen for cellular respiration and growth but is not harmed by oxygen. It relies on fermentation metabolism, a process that converts sugar to acids, gases or alcohol and leads to the production of energy. (15)
Reproduction and Life cycle/Growth and Development
two stages: cyst and trophozoite
cyst:
approximately 7-10 µm in length, oval in shape, has
responsible for the disease transmission of giardiasis
after ingestion, the cysts, located in the small intestines, release trophozoites through a process called excystation
trophozoite:
approximately 7-10 µm in length and resemble a teardrop, have two distinct nuclei and four pairs of flagellae
responsible for producing the clinical disease in humans
colonize in the small intestine and can multiply through longitudinal binary fission, a form of asexual reproduction in which the parent cell divides into two identical daughter cells. The cycle repeats after the trophozoites move toward the colon.
trophozoites retreat back into their cyst stage in a process called encystation and new cysts are then excreted in the feces. (1)
(7)
Integument
a tough outer shell enables it to survive outside the human body and also makes it resistant to disinfectants containing chlorine. (3)
Movement
trophozoites have four pairs of flagella that allow the organism to move with a rotating motion
the anterior and posterolateral flagellum act like oars to propel the body forward
the ventral flagellum beat in a wave motion
the flagella work together for directional control (18)
Giardia lamblia flagella
Sensing the environment
pancreatic protease, cysteine protease CP2 and acidic conditions facilitate excystation
the presence of fatty acid conjugated with bile salts and mildly basic conditions facilitate encystation (19)
Gas exchange
occurs by diffusion, in which oxygen diffuses directly across the membrane and into the organism (10).
Waste removal
after the food enters the cell and is digested in the vacuole, waste products are excreted by exocytosis, a process by which a vesicle inside the cell moves towards the plasma membrane and fuses with it, expelling its contents
Environmental physiology (temperature, water and salt regulation)
lives and breeds in warm moist places, but because of its hard outer shell, it can survive in a variety of temperatures
cysts can survive at temperatures as low as 4 degrees Celsius and as high as 25 degrees Celsius for several weeks, allowing it to inhabit soil, food, contaminated water, and feces. Depending on the substance they reside in, they can survive longer. For example, Giardia can survive 11 weeks in water, but only 1 week in cattle feces. (3,5)
Internal circulation
no complex circulatory system because the organism is unicellular
semipermeable membrane allows for nutrient intake and vesicles excrete wastes
Chemical control (i.e. endocrine system)
no endocrine system because the organism is unicellular
ReviewQuestions:
1.Why is Giardia Lamblia so dangerous to humans?
2. How can Giardia Lamblia survive in the human body despite the immune system?
Classification/Diagnostic characteristics
Domain: Eukarya
Kingdom: Protista
Phylum: Sarcomastigophora
Class: Zoomastigophora
Order: Diplomonadida
Family: Hexamitidiae
Genus: Giardia
Species: lamblia
Relationship to humans
Habitat and niche
Predator avoidance
Nutrient acquisition
Reproduction and Life cycle/Growth and Development
Integument
Movement
Sensing the environment
Gas exchange
Waste removal
Environmental physiology (temperature, water and salt regulation)
Internal circulation
Chemical control (i.e. endocrine system)
Review Questions:
1.Why is Giardia Lamblia so dangerous to humans?
2. How can Giardia Lamblia survive in the human body despite the immune system?
References
1. http://www.giardiasis.org/Giardia-Lamblia.aspx2. http://davisjscientist5.blogspot.com/2008/02/giardia-lamblia.html3. http://www.cdc.gov/parasites/giardia/index.html
4. https://www.msu.edu/course/zol/316/glamtax.htm
6. http://www.phac-aspc.gc.ca/lab-bio/res/psds-ftss/giardia-lamblia-eng.php
7. http://upload.wikimedia.org/wikipedia/commons/thumb/d/db/Giardia_life_cycle_en.svg/619px-Giardia_life_cycle_en.svg.png8. http://www.cdc.gov/parasites/giardia/9. http://www.syncytiabeta.org/~syncyt5/syncytiabeta/images/c/ce/Giardia.jpg10. http://www.pcsd.k12.ny.us/bwoods/Regents%20Biology/Chapter%2011%20Gas%20Exchange/Chpter%2011%20Gas%20Exchange.htm11. http://water.me.vccs.edu/courses/env108/lesson6_2.htm12. http://emedicine.medscape.com/article/176718-overview13. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC88984/14. http://www.tulane.edu/~wiser/protozoology/notes/disk.html
15. http://www.ncbi.nlm.nih.gov/pubmed/6108507
16. http://www.dpd.cdc.gov/dpdx/images/ParasiteImages/G-L/Giardiasis/Giardia_cyst_wtmt3.jpg
17. http://www.answersingenesis.org/articles/am/v7/n1/magnificent-motors
18. http://www.ncbi.nlm.nih.gov/pubmed/21808023
19. http://microbewiki.kenyon.edu/index.php/Giardia_lamblia#Metabolism
BSCS Biology. a Molecular Approach. New York: Glencoe/McGraw-Hill, 2006. Print.